This invention relates generally to propulsion systems and, more particularly, to an engine mounting assembly for a marine propulsion system.
Mechanical propulsion systems for propelling watercraft generally are classified as either outboard systems or inboard systems. Outboard systems typically are characterized by an outboard motor mounted to a vertical transom plate located on an outside stern of a boat hull. A propeller drive unit is attached to the motor, or powerhead, and extends from the powerhead into the water to generate thrust and propel the watercraft. Outboard motor systems are versatile, compact, and costeffective units that are relatively easy to install on the boat hull. Also, because the outboard system is attached to the outside of the hull, the outboard motor system generally does not occupy interior space of the boat hull. However, due to structural constraints of the vertical transom plate mounts of outboard systems, watercraft with outboard systems are typically limited to certain motor capacities within size and weight constraints.
Inboard systems are typically characterized by larger, complicated, and relatively expensive engines in comparison to outboard systems. Inboard system engines are mounted in an engine compartment in a boat hull interior, and a drive unit, or stem drive, extends through a vertical wall of the boat hull into the water to generate thrust and propel the watercraft. Inboard systems, however, are much more complicated to install in a boat hull, which further increases the cost of a watercraft. Furthermore, bulky inboard engines and engine compartments often occupy a substantial amount of interior hull space due to the proximity of the engine compartment to a running surface of the hull.
In an exemplary embodiment of the invention, a marine propulsion system includes an outboard propulsion system powerhead mounted to a horizontal mounting plate in an outside engine compartment enclosed by an engine cover. The marine propulsion system includes an upper unit that includes the powerhead and a lower unit that includes a propeller drive unit. A four point mounting assembly eases installation of the upper and lower units and absorbs vibration of the upper and lower units to produce smooth, quiet propulsion of a watercraft. The outboard powerhead is mounted stationary to the horizontal mounting plate, and a steering arm yoke and trunnion assembly is attached to the horizontal mounting plate and to the propeller drive unit.
More specifically, the mounting assembly includes the horizontal mounting plate, a pivot housing attached to the horizontal mounting plate, and an adapter plate attached to the pivot housing. The horizontal mounting plate includes a recessed surface defining a central opening therein that is received in a recess through a watercraft platform extending from a hull of the watercraft. A shoulder surrounds the recessed surface and includes attachment holes for attachment to the platform. The opening in the horizontal mounting plate is contoured to allow drop down installation of the marine propulsion system.
The pivot housing includes a central drum and a plurality of mounting brackets extending therefrom for attachment to the horizontal mounting plate. A central opening extends through the drum, and the drum extends through the central opening of the horizontal mounting plate. The steering arm yoke is internally mounted into the central drum, which forms a mounting surface for attachment of a steering arm. The yoke and steering arm rotate about an axis of the pivot housing which allows the marine propulsion system lower unit to rotate and maneuver the watercraft.
The adapter plate includes a powerhead mount portion having a central opening therethrough for a drive shaft of the powerhead, an exhaust portion configured for mounting of an exhaust system, and a plurality of brackets extending from the powerhead mount portion and the exhaust mount portion for attachment to the pivot housing. The adapter plate further includes cooling water ports and passages for the powerhead and exhaust systems, and telescoping drums extending through the mount portion central opening. The telescoping drums are received by the pivot housing central opening, and the powerhead drive shaft extends through the telescoping drums. The telescoping drums secure main drive bearings which support a main drive shaft of the marine propulsion system.
The horizontal mounting plate, pivot housing, and adapter plate are attached to one another at four isolation points that include shock absorbing and vibration absorbing drive mounts and engine mounts, respectively, to reduce vibrations between the upper and lower units of the marine propulsion system, and to reduce transmission of vibration to the watercraft platform through the horizontal mounting plate.
The marine propulsion system upper and lower units, including the outboard powerhead, the mounting assembly, the steering arm yoke and trunnion assembly, gear shift mechanism, gearcase, and propeller, are fully pre-assembled and tested, and the assembly is lowered through a-recess in the watercraft platform. The horizontal mounting plate is secured horizontally to the platform, and installation is completed by making hydraulic connections for trim, tilt, and steering of the propeller drive unit, and by making appropriate fuel, electrical and control system connections to the various components of the propulsion system.
Thus, the mounting assembly provides a marine propulsion system with the versatility, compactness and cost savings of an outboard powerhead and the stability and performance advantages of an inboard system. Structural limitations and instability of vertical horizontal mounting plate mounts are avoided by mounting the outboard powerhead to the horizontal mounting plate. Drop down installation of preassembled propulsion system components greatly simplifies installation in comparison to conventional inboard systems which, when combined with cost savings of an outboard powerhead, substantially reduces the cost of a completed watercraft.